In certain types of signal transmission systems, such as communications satellites, it is necessary to couple energy from a plurality of microwave signal sources to a single output port. Waveguide-based systems use various types of variable ratio power combiners that operate essentially as variable directional couplers providing selective coupling from zero to 100%. One such waveguide-type variable ratio power combiner is described and claimed in U.S. Pat. No. 4,492,938, which is assigned to the assignee of the present invention. This device provides the variable combining feature by mechanical adjustment of its waveguide components.
Recent advances in solid state technology have made it possible to replace, at some frequencies, vacuum tube high-power amplifiers with solid-state high power amplifiers. Although the solid state high power amplifiers provide higher reliability, they have sharply limited power handling capabilities, compared to vacuum tube high power amplifiers. Accordingly, power combiner circuits are used with the solid state devices to provide suitably high levels of power transmission.
A schematic block diagram of a typical solid-state high power amplifier is shown in FIG. 1 as containing the following principal elements: a power divider section 12, a solid state amplifier section 13, and a power combiner section 14, coupled in cascade between an input port 11 and an output port 15. In general, the power combiner section 14 is a replica of the power divider section 12, except for higher power physical considerations. The number of individual amplifier modules 13-1 . . . 13-N will depend upon the capacity of a single module 13-i, the total output required, and the losses through the power divider section 12 and the power combiner section 14. There are many types of signalling and coupling hardware that can be used for the divider and combiner sections illustrated in FIG. 1. Included among these couplings schemes are stripline networks using Wilkinson type dividers, waveguide or coaxial networks using 3 dB quad couplers, ratio combiners having a center coaxial probe, and ratio coaxial feed probes contained within a parallel plate structure.
A prior art 3 dB hybrid directional coupler 16 is illustrated in FIG. 2; the coupler 16 can be implemented in microstrip or stripline. When a signal is provided as an input to a egment 17, the segment 18 is isolated, i.e., no part of the input signal appears at the isolated segment 18. A segment 19 carries one-half of the input signal from the segment 17 with a relative output phase of 0.degree. and a segment 20 carries one-half of the input signal with a relative output phase of 90.degree.. As can be seen, a connecting segment 21 bridges the segments 17 and 19 with the segments 18 and 20.
The prior art microwave power dividers, such as those mentioned above, are individually designed and constructed to achieve specific fixed divisions of the input microwave power at the output ports. Once one of these microwave power dividers has been designed and constructed to achieve a specific power split, it cannot later be easily changed to give a different power split. For example, if a magic T or hybrid coupler has been designed and constructed to achieve a 3/3 dB power split in which one-half of the input power is seen at each of the two output ports, it cannot thereafter be changed to achieve a 6/1.25 dB, in which one-fourth and three-fourths of the input power is seen at the two output ports.
A prior art circulator 36, which can provide limited power combining/dividing, is illustrated in FIG. 3. The circulator 36 has 3 ports designated by reference characters 38, 40, and 42. The application of a static external magnetic field allows an input signal at one port to be reflected to an output at a different port. For example, when a signal is input to port 38 the output signal appears at port 42, and port 40 is isolated. When a signal is provided as an input to the port 42, the output signal appears at the port 40 and port 38 is isolated. Lastly, when a signal is provided as in input to port 40, the output signal appears at port 38, and port 42 is isolated. The circulator 36 is not a power-efficient device, but it can be electromagnetically adjusted to provide limited power division among the ports. Limited power division around a nominal value can be obtained by adjusting the magnetic field intensity orthogonal to the circulator substrate. Power division can also be accomplished by connecting a variable impedance between one port of the circulator 36 and ground. Changing this impedance value will change the power ratios.